The present invention relates to a developing device and, more particularly, to a rotary multi-color developing device applicable to, for example, a color electrophotographic copier having a plurality of developing units which are movable in a rotational motion to a predetermined developing station. The present invention also relates to a developer supply device for feeding toner, or developer, from a toner tank by a toner feed member which is operated within the tank, thereby supplying the toner to a developer chamber of the developing device.
A rotary multi-color developing device is disclosed in, for example, U.S. patent application Ser. No. 039,741 filed Apr. 20, 1987 and assigned to Ricoh Company Ltd., and such a type of developing device has been applied to a color electrophotographic copier and other image-forming apparatuses. In this type of developing device which uses a two-component developer, i.e., a mixture of toner and carrier, toner is transferred to a photoconductive element, or image carrier, to be sequentially consumed as the developing operation is repeated. Hence, additional toner has to be replenished to a developer chamber of the device as occasion arises. This is implemented with a toner supply conduit which extends from a toner supply device which is provided with a toner tank. In this instance, because toner is poorer in fluidity than carrier, should toner be fed alone through the toner supply conduit, its transport might be impaired. In the light of this, it has been customary to form some openings through the toner supply conduit in order to introduce into the conduit a developer which includes carrier and is stored in the developer chamber, the carrier being mixed with toner which is fed from the tank. This allows the toner to be transported with enhanced fluidity and discharged together with the carrier from an outlet of the conduit. Such a toner supply conduit is disclosed in, for example, Japanese Laid-Open Utility Model Publication (Kokai) No. 56-74457/1981. However, simply providing openings in the toner supply conduit as mentioned above fails to allow the toner to flow into the conduit with efficiency. Specifically, because a sufficient amount of developer cannot be introduced into the conduit, it is difficult for the developer inside the conduit to attain a desired degree of fluidity.
Meanwhile, the toner supply device is constructed such that toner stored in the toner tank is fed out by a toner feed member which is disposed in the tank, the toner being transported through the toner supply conduit to the developer chamber. The toner tank, too, has to be replaced with a new one when it is exhausted or substantially exhausted due to repeated developing operations. A problem heretofore pointed out with this kind of toner supply device is that a toner end sensing and displaying means which urges an operator to replace the toner tank is considerably complicated in construction and, therefore, expensive.